Trunk circuit



H. C. ALTHOUSE Aug. 20, 1957 TRUNK CIRCUIT 2 sheets-sheet 1 Filed sept.20,' 1955 IBI.

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ATTORNEY Aug. 20, 1957 H. c. ALTHoUsE TRUNK CIRCUIT 2 Sheets-Sheet 2Filed sepi. 20, 1955 /N VEN Ton H. G. A L THOUSE A TTOR/VE V Patented20, M95? A 'Nice American rtelephone and poration of New York d.,assigner to Telegraph Company, a toru Application September 20, 11955,Serial No. 535,393 s oisans. (ci. ironia) This invention relates totelephone switching systems and more particularly to such systemscomprehending the interconnection of two or more central oiices bytrunks commonly usable for toll and non-toll services.

In certain telephone systems, automatic recording devices have beenprovided to more economically record individual subscribers service, andto prepare the usual billing from such records. The cost of suchrecording equipment, however, is substantial; and in order to justifythe necessary capital investment, it is desirable that a large number ofsubscribers stations be served by each recording unit. Accordingly, insome instances, it has been found necessary to connect a plurality ofsmall central ofhces to a centrally located switching center in orderthat the advantages of the automatic recording equipment located at suchcenter may be made available to a large number of subscribers.

At certain of such small central ofdces, the volume of traiiic directedto the centralized switching center may be `of such small magnitude thatonly a minimum number of interconnecting trunks may be economicallyjustified. ln such cases, it is advantageous to make such trunksavailable both to operators and to individual subscriber Consequently itis requisite that some provision be made to permit both thenon-chargeable and chargeable use of such trunks, the subscribers beingpermitted use thereof on `a chargeable basis, whereas the operators arvgiven across thereto without charge.

In small oiices having `the well-known step-by-step type equipment, itis anticipated that a subscriber might gain access to one of theaforementioned trunks by dialing a directing code, for example, 11. Athird digit would then be dialed and transmitted along the Itrunk to theswitching center, at which the trunk would be connected to another trunkextending in the desired direction and, of course, to the recordingequipment. .For the operator to gain access to such switching centerover the same tracks, and to other trunks thereat for the establishmentof nocharge connections, it is anticipated that operators would transmita different third digit, thereby establishing a unique path from thetrunk into the system without ob taining access to the recordingequipment. However, is likely that subscribers eventually would discoverthe identity of the operators third digit, and that, instead of dialingthe proper third digit yassigned for subscribers use, some of them mightdial the operators digit andl the; ny gain access at the switchingcenter at an outgoing trunk over which a connection could be establishedto any telephone station in the United States without incurring theappropriato charge therefor.

It is therefore an object of this invention to provide discriminatorycircuit to be interposed between the loca central other, and each of theaforementioned trunks to the switching center, whereby subscribers cailsotherwise placeable on a nonchargeable basis would be intercepted.

Accordingly, in .accordance with one feature of this invention, acut-through relay is interposed between the local central ofce and theaforementioned trunk circuit to divert the extension of a subscriberscall in response to `the subscribers dialing of the operators code.

ln accordance with another feature of this invention, a begin-pulse andan end-pulse relay are interconnected with ia maintain-cutethrough relayto control operation of the cut-through relay in response to receptionof dial pulses.

These and other objects and features of this invention will be apparentfrom the following detailed description, by way of example, withreference to the drawing in which:

Fig.- l is a semiblock diagram depicting the relevant components of theaforementioned local central office equipment :and the tandem switchingoffice; and

Fig. 2 is a schematic diagram setting forth in detail the diversioncircuit of Fig. 1 and associated control devices.

Referring, now, to Fig. l, it will be noted that a connection is showntrom a subscriber to a first selector switch of the wellknownstep-bystep type. lf the subscriber initially dials the digit 1, thisfirst selector will step to the rst level and rotate in the conventionalmanner to locate a path to an idle auxiliary selector. lf the customerthen dials a second digit 1, the auxiliary selector will step to the rstlevel and similarly rotate to find a path to an idle diversion circuit,thereby extending conductors tip (T), ring (R), sleeve (S) and (A) ofthe seiector to the two-way trunk, the tip (T) and ring (R) conductorsthereof extending to the tandem switching ciiice. The diversion circuitismore particularly illustrated in the schematic diagram of Fig. 2;however, in advance of a detailed description of this circuit, it willbe helpful to understand the functioning thereof with respect to theremaining devices depicted in Fig. l.

As hereinbefore mentioned, the dialing of a third digit will be requiredto extend connections over a two-way trunk to the tandem switchingcenter, and it will be further noted from Fig. 1 that both the operatorand the subscriber may have access to this trunk by way of the commontwo-way trunk. The third dialed digit will control the code selector atthe tandem switching office at which the trunk terminates. lf the thirddigit is 1, the selector will rise to the first level and then rotate tolocate a non-charging trunk. On the other hand, if the third dialeddigit is 2, the aforementioned code selector will step to the secondlevel and rotate to find a charging trunk leading out of the office.This charging trunk has access to AMA recording equipment (not shown)that will record the details of the established connection.

It is desired to intercept customer dialed calls which might passthrough both the local and tandem oiiices without charge; it istherefore proposed to interpose the diversion circuit mentioned abovefor preventing free connections in response to the dialing of theoperator code by such customers.

In Fig. 1, the arrow leading from the tandem switching olhce (CAMA) tothe two-way trunk circuit indicates that calls may be directed in thereverse direction over the trunk circuit.

Turning, now to Fig. 2, it will be noted that conductors El, T, S, andA, identified as lli), 1i, l2, and i3, respectively, are shown enteringthe diversion device from the auxiliary selector. Conductor A is merelyextended through the device to the two-way operator ofce trunk. lnresponse to dialing of the second unit digit, sleeve conductor l2 isgrounded in the conventional manner,

c thereby extending a path from ground, conductor M,

through the No. 3 back contacts of relay f7, the coil of relay 18, andthence to negative battery. Relay l operates in this circuit and extendsring and tip condoctors i@ and 1l through its Nos 2 and 3 front contactsto outgoing ring and tip conductors 2li and Z2, respectively, extendingthe dialing loop to both windings of the trunk pulsing relay 9b, overthe left windings of repeating coil RC1 and the contacts of relay 75.Relay 90 operates over the loop, closing over its Nos 2 and 3 contacts,conductors R and T and booster battery and ground to the winding of apulsing relay (not shown) in the code selector at the tandem office.Over its No. l contacts, relay 90 removes ground from lead 23.

The subscriber now dials the aforementioned third digit and pulsesaccording to the dialed numeral are transmitted Via conductors and 11,the Nos. 2 and 3 front contacts of relay 18, conductors 21 and 22, theNos. 1 and 4 back contacts of relay 75, the primary windings ofrepeating coil RC1, and the Nos. 2 and 3 back contacts of relay 75 tothe coils of pulse repeating relay 98, and thence to battery and ground.Relay 90 faithfully reproduces the dial pulses and correspondingly opensand closes the trunk loop over its Nos. 2 and 3 front contacts to thepulsing relay in the code selector at the tandem switching oce. Inaddition, it controls operation of relay 19 over the path from ground,the No. 1 contacts of relay 90, conductor 23, the coil of relay 19 andsource of negative potential 20.

Circuitry illustrated in Fig. 2 as part of the two-way operator-otticotrunk, is merely representative of one arrangement thereof which is wellknown in the art and to which reference may be made in Patent No.2,268,635 which was granted to John Baumfalk et al. on January 6, 1942.1n the interest of clarity, relays 75 and 90 of Fig. 2 are similarlyidentied in the drawing of the referenced patent. Although the backcontacts l of relay 90 lare not disclosed therein, it will be recognizedthat such contacts could be readily added thereto. As will be noted bythose skilled in the art, other two-way operatonofce trunks orpath-extending devices could be employed to extend talking paths, and torepeat dial pulsing for operation of the diversion circuit relays.

Returning, now, to the operation of the diversion circuit of Fig. 2, ifthe third dialed digit is 1, relay 19 will ybe energized and releasedonce, and operation will be according to the description immediatelyfollowing, whereby connections are routed to the intercept device. Onthe other hand, if the third dialed digit is 2, relay 19 will beenergized and released twice, and operation will be according to thedescription hereinafter noted, wherein talking paths are extended to thetandem ofce at which a toll trunk is suitably seized.

1f the third digit is 1, relay 19 will operate at the beginning of thepulse and complete a path over its front contacts and the No. 1 contactsof relay 17 to the coil of relay 16, and thence to negative battery. Inaddition, the path is extended to the coil of relay 17 and thence viathe No. 3 front contacts of relay 16 and conductor 16 to the incomingsleeve lead 12 which, as previously mentioned, is grounded by thepreceding apparatus. Accordingly relay 16 operates, but relay 17 remainsunoperated since ground is connected to both terminals of its operatingcoil. At the end of the first pulse, relay 19 is deenergized and itscontacts open, thereby breaking the path from ground over the No. 1contacts of relay 17 to the relay 17 operating coil. Relay 17 nowoperates over a path from battery 28, relay coil 16, the coil of relay17, the No. 3 contacts of relay 16, conductor 14, and grounded sleevelead 12, the characteristics of relays 16 and 17 being such that bothwill opcrate when their coils are serially connected to the source ofoperating potential 2t). Relays 16 and 17 are now locked to ground viathe previously mentioned No. 3 contacts of relay 16. The No. 3 contactsof relay 17, in opening, interrupt the path from ground to the coil ofrelay 18, causing the latter relay to become deenergized, and therebycausing the incoming ring and tip conductors 1@ and 11 to be transferredfrom the outgoing trunk conductors 21 and 22 to conductors 241 and 25,respectively, the latter serving to extend the path via the Nos. l and 2front contacts of relay 16 to the intercepting device. Thus a subscriberdialing the prohibited operated code 111 is prevented from gainingaccess to the commonly used trunks and is instead suitably diverted toan intercept device.

When the subscriber disconnects his instrument from the line, ground isremoved from sleeve conductor 12, thereby resetting relays 16 and 17 tothe normal condition.

it is desired that connections be extended through to the tandemswitching oce when the subscriber dials the proper third digit, i. e.,2, and such operation of the circuit will now be described.

As before, the step-by-step equipment connects sleeve conductor 12 toground, thereby operating relay 18 over the previously described path.Pulsing relay 19 now operates in response to the first pulse of thethird dialed digit and extends paths as hereinbefore described tooperate relay 16. At the end of the first pulse, relay 19 is deenergizedand opens the path from ground to the coil of relay 17, thus operatingrelay 17 in series with relay 16Vas explained above. rThe No. 3 contactsof relay 17 now open the path from the coil of relay 18 to ground andrelay 18 contacts tend to become disengaged; however, characteristics ofthe relay are such that its contacts release very slowly, and beforethey change electrical condition, the second operating pulse is receivedat the coil of relay 19, thereby operating same and extending a pathfrom ground over the front contacts thereof and the No. 2 front contactsof relay 17 to the operating coil of relay 15 and thence to negativebattery 20, thereby energizing and operating relay 15. in operating,this relay extends ground from sleeve lead 12 over conductor 14 and itsNo. 2 front contacts to the operating coil of relay 18, thusreenergizing relay 18 before the contacts thereof have changed position.in addition, relay 15 locks itself to ground via sleeve lead 12 andconductor 14 over its own No. l front contacts, thus assuring thecontinuity of an operating path to relay 18 so long as the connection ismaintained by the calling subscriber.

Relays 15, 16, 17, and 18 are now locked to ground over sleeve conductor12 and will remain operated until reset in response to subscriberdisconnect. The trunking path comprising ring and tip conductors 10 and11 will therefore be extended through the Nos. 2 and 3 front contacts ofrelay 18 and conductors 21 and 22 to the aforementioned trunk circuit.Subsequent customer dialing will have no effect upon the diversioncircuit because the No. 1 contacts of relay 17 are open, and furtherbecause ground already -appears at the contacts of relay 19 from thesleeve lead over conductor 14, the No. 1 front contacts of relay 15, andthe No. 2 front contacts of relay 17. The presence of this ground willkeep the above relays operated regardless of the subsequent pulsingoperations of relay 19.

in addition to the functions hereinbefore said to be performed by relay16, contacts 1 and 2 thereof are interposed in the paths leading fromconductors 24 and 25 to the intercepting device, which in some cases maybe a tone source, in order to prevent introduction of tone potential onto ring and tip conductors 1t) and 11 when the diversion device is idle.Were relay 16 contacts not thus interposed, paths would lie from thetone source via conductors 24 and 2S, the Nos. 2 and 3 back contacts ofrelay 18, and conductors liti and 11 to the auxiliary selector.

One additional function performed by relay 18 comprises the completionof a path from sleeve conductor 12 via conductor 14, the No. 3 frontcontacts of relay 16, the No. l back contacts of relay 18 and `conductor26 to the intercept device during the period of interception.

Specic types of relays contemplated by the hereinbefore describedembodiment are unimportant except for the following characteristicsthereof. Relays 15, 16, 17, and 19 may, for example, be of the`conventional telephone type with characteristics of relatively rapidoperation and release. Relay 18, however, should have a slow release andrapid pick-up characteristic in order that it may ride over themomentary deenergization hereinbefore set forth.

Although the subject invention has been illustrated by a particularembodiment thereof, the invention is not limited to the specificcircuits therein disclosed. Various applications, modications andarrangements of the invention will readily occur to those skilled in theart. For example, the customers third dialing digit could be any numbergreater than one.

The terms and expressions hereinbefore employed in reference to theinvention are used as terms of description and not of limitation; andthere is no intention in the use of such terms and expressions ofexcluding equivalents of the features shown and described or partsthereof, but on the contrary it is intended to include therein any andall equivalents, modifications and adaptations which may be employedwithout departing from the spirit of the invention.

What is claimed is:

1. In a telephone system, a trunk terminating in a selector having twooutlets, said trunk having two points of access at its originating end,means responsive to a first dial pulse code transmitted from one of saidpoints of access for operating said selector to engage one of saidoutlets, means responsive to a second dial pulse code transmitted fromthe other of said access points for operating said selector to engagethe other of said outlets, and means connected to said other of saidaccess points responsive to said first dial pulse code transmitted fromsaid other of said access points for blocking the elective operation ofsaid selector.

2. In a telephone system, a path diverting device comprising an inletand two outlets, a first relay for controllably extending paths fromsaid inlet to said outlets, a second relay responsive to subscriberdialed pulses, a third relay responsive to the initial pulse received bysaid second relay, a fourth relay responsive to the termination of saidinitial pulse, and a fifth relay responsive to the second pulse receivedby said pulsing relay, said first relay being controlled by said otherrelays to establish and maintain paths from said inlet to one of saidoutlets in response to reception of only one electrical impulse by saidsecond relay, or to establish and maintain paths from said inlet to theother of said outlets in response to reception of two or more electricalimpulses by said second relay.

3. In a telephone system, a trunk, means for connecting operators anddialing subscribers to the originating end of said trunk, means forconnecting a binary selector to the terminating end of said trunk, saidbinary selector aeoavoe being operable in response to a first impulsecode transmitted over said trunk to extend connections from said trunkto an outlet, said binary selector being further operable in response toanother impulse code transmitted over said trunk to extend connectionsfrom said trunk to another outlet, and means responsive to one of saidcodes for diverting connections from said trunk to an interceptingdevice.

4. In a telephone system, a device for preventing free customertelephone calls, comprising a trunk commonly available for chargeableand non-chargeable service, said trunk terminating in a selecting devicehaving two outlets, one of said outlets having automatic recordingapparatus connectable thereto, said selecting device being controllableto extend a connection from said trunk to additional switching appartusvia said one of said outlets in response to the actuation of saidselecting device by a rst predetermined code expressing a chargeableconnection, said selecting device being also controllable to extend saidconnection to said switching apparatus via the other of said outlets inresponse to actuation thereof by a second predetermined code expressinga free call, and circuit diverting apparatus serially interposed inpaths connecting a chargeable subscribers line to said trunk fordiverting the path otherwise leading from said line to said trunk inresponse to the activation thereof by said second predetermined code.

5. In a telephone system, a path diverting device having an input andtwo outputs each comprising tip, ring and sleeve conductors, acut-through relay for controllably extending paths from said input tosaid outputs, a pulsing relay responsive to subscriber dialed pulses, abegin-pulse relay responsive to the initial pulse received by saidpulsing relay, an end-pulse relay responsive to the termination of saidinitial pulse, and a maintain-cut-through relay responsive to the secondpulse received by said pulsing relay, said cut-through relay beingcontrolled by said other relays to establish and maintain paths fromsaid input conductors to one of said outputs in response to thereception of two or more electrical irnpnlses by said pulsing relay, orto establish and maintain paths from said input conductors to the otheroutput in response to reception of only one electrical impulse by saidpulsing relay.

References Cited in the iile of this patent UNITED STATES PATENTS2,586,534 Gray Feb. 19, 1952 2,673,243 Lomax Mar. 23, 1954 2,733,295Lomax Jan. 31, 1956

